The invention relates generally to water treatment, and, more particularly, to a technique for measuring hardness of water and using such measurements.
Industrial and residential water systems draw water from a number of potential sources including wells, rivers and reservoirs. These sources have varied levels of inherent water hardness. Water hardness is generally a function of calcium (Ca) and magnesium (Mg) concentration. It is measured in grains per gallon or milligrams per liter of calcium carbonate and can vary from 0 to greater than 50 grains per gallon depending upon the water source.
Calcium and magnesium species responsible for hardness in water also account for much of the inorganic scaling and fouling of water in industrial and residential water systems and appliances. Fouling of water has been observed in residential environments, such as, for example, in sinks, tubs, dishes, glassware and also hot water heaters. Similarly, in industrial systems, fouling of industrial boiler systems and heat exchangers has been observed. Hardness of water also commonly affects performance of detergents in cleaning or washing applications. Elevated levels of water hardness also affect the performance and maintenance of water softeners.
Some of the widely used techniques for measuring hardness of water include calorimetric, fluorescent assays that measure concentrations of calcium and magnesium. Colorimetric and fluorescent assays are tested by addition of liquid or solid reagents to a water sample that is buffered to an appropriate pH. The reagent addition either includes a one step addition, wherein a final color is measured, or is performed as a titration, and wherein a point of color transition is determined. The assays are then measured with a photometric detector followed by disposal of the sample and spent reagents.
However, the colorimetric assays and fluorescence assays are relatively labor intensive to test and are principally used for periodic or point measurements. In addition, the reactions involved in such testing are irreversible and the sample and test strips often used for such testing are thus disposed of following the measurements. This makes their use in industrial, commercial, and particularly consumer appliances impractical.
Further, the availability of water of variable hardness commonly requires a user of home appliances, such as clothes washers and dishwashers, to manually adjust the amount of detergent to achieve optimal cleaning of clothes and dishes. In general, the quantity of detergent required increases with the hardness of water so as to achieve optimal performance. However, manually adjusting the amount of detergent based on an assumption that is likely to incorrectly reflect actual hardness of water commonly leads to waste of detergent or, conversely, to the use of insufficient detergent when hardness is particularly elevated.
In another application, such as controlling regeneration of a water softener, it has been assumed that hardness levels of influent water to a water softener are constant. However, for all practical purposes, the hardness level of influent water is a variable quantity. Further, regeneration control systems of water softeners commonly measure volume of water treated as the only control variable. Hence, varying hardness levels of water can adversely affect performance of the water softeners in a manner not compensated for by the control algorithms.
Hence, an improved technique for measuring hardness of water is needed to address the aforementioned issues. It would also be desirable to provide a technique to monitor hardness of influent water in real time in home appliances and water softeners for optimal performance.